Why 1964 and 1977?

Well, the year 1964 comes from the combination of the initial 28-year term and the fact that renewal was made optional in June 1992 by P.L. 102-307, 106 Stat. 264. Before 1992, a copyright holder was required to renew a copyright after 28 years, otherwise the work went into the public domain. So if a work was published in 1964, it would have had to be renewed in 1992 (1964 + 28 = 1992) -- but in 1992, the renewal requirement was abandoned, so renewal didn't matter. Basically, 1964 is the first year to take advantage of the optional renewal. The year 1977 comes from the fact that the Copyright Act of 1976 became effective January 1, 1978; 1977 was the last year for the old law's scheme, of multiple terms based on publication, to be used.  more